The issue is not whether the shelling is justified. It clearly is justified when the Arabs are shelling Israel first and won't stop. The issue is that it is wholly ineffective, and prone to errors like this. The best method is to use commandos and undercover specialists to kidnap and make precision hits. Arab killers should be taken alive if possible and held incommunicado, no announcements, no press coverage, to install fear in the enemy. They simply disappear, forever.
Three Palestinian teens killed by Israeli army fire during protests near Gaza border (Haaretz)
from the article: Peretz: Gaza beach blast may have internal Palestinian cause